Method of opening an intermediate vessel nozzle for continuous casting

ABSTRACT

A method of and apparatus for handling liquid steel in a tundish preparatory to teeming the steel into a continuous casting mold. Initially the tundish outlet is closed with a slidable gate which has a porous plug aligned with the outlet. Inert gas is injected into the steel through this plug to agitate the steel in the region of the tundish outlet. Inert gas injection is terminated shortly before the commencement of teeming, and oxygen rich gas is injected to react exothermically with the steel in the nozzle well area. Thereafter the porous plug slidable gate is replaced with a conventional gate having a teeming opening.

United States Patent [1 :1 3,809,146 Andrzajak et al. May 7, 1974 METHOD OF OPENING AN 3,581,948 6/1971 Detalle .j. 266/34 PP x INTERMEDIATE VESSEL NOZZLE FOR 3,684,267 8/1972 Andrzejak et al. 266/38 CONTINUOUS CASTING 3,773,226 11/1973 Kutzer 222/148 [75] Inventors: Sigmund L. Andrzajak, Chicago,

111.; Michael A. Orehoski, Duquesne; Primary Examiner-Robeft Baldwin James T. Shapland, Wilkins Attorney, Agent, or Firm-Ralph l-l'. Dougherty Township, Allegheny County, both of Pa.; Raymond S. Szumilas, Chicago, I". 57 ABSTRACT I [731 Assignee: United States Steel Corporation, p

Pittsburgh p A method of and apparatus for handling liquid steel in a tundish preparatory to teeming the steel into a con- [22] plied: 1972 tinuous casting mold. Initially the tundish outlet is [21] App1.No.: 227,476 closed with a slidable gate which has a porous plug aligned with the outlet. Inert gas is injected into the steel through this plug to agitate the steel in the region [52] 164/66 164/82 266/34 PP of the tundish outlet. Inert gas injection is terminated [51] Int. Cl B2211 11/10 shortly before the commencement of teeming, and [58] Field Of Search 164/66, 82; 266/34 PP, ygen i gas i injected to react exothermicany with 266/38; 222/DIG- 13 the steel in the nozzle well area. Thereafter the porous plug slidable gate is replaced with a conventional gate [56] References C'ted having a teeming opening.

UNITED STATES PATENTS 3,320,053 5/1967 Lehman 75/59 4 Claims, 1 Drawing Figure OXYGEN PATENTEDMY 7 I974 mumr 6A5 OXYGEN 1 METHOD OF OPENING AN INTERMEDIATE VESSEL NOZZLE FOR CONTINUOUS CASTING In the continuous casting of steel, molten'metal is poured from a ladle into an intermediate pouring vessel, suchas a tundish or a degassing vessel, andthence into a water-cooled mold. The refractory lining of the intermediate vessel is usually recessedabove the nozzle, andthe nozzle is closed by a refractory closure member, such as a sliding gate. The metal that-first reaches this recess has already lost much of its heat to the refractory lining of the vessel. This rather quiescent metal settles into the recess, loses additional heat to the surrounding refractory and begins to solidify. The molten metal in the vessel above the recess does not contain sufficient superheat to remelt the solidified metal. Openingthe blocked recess heretofore has necessitated the use of an oxygen lance, which is an undesirable practice as it may impair the quality of the metal and damage refractories of the intermediate vessel. Whenever pouring is interrupted by closing the nozzle, molten metal in the recess above the nozzle cools more rapidly than the metal above it because it has a larger surface area in contact with the surrounding refractory, that is, it has a higher surface-to-volume ratio. The cooling action of the refractory can result in the formation of frozen steel or"skull in the nozzle region and prevent stream flow when the nozzle is reopened; The present invention affords a methodof preventing a re' cess from blocking, either before pouring begins or when pouring is interrupted.

It is known thatinert gases can be introduced to molten metal to provide various treatments. For example,

. 2 valve. 23. Ifjacket 17 is made ofrnore than one piece, it must be tightly welded to preventany gas leaks, either through the jacket itself or between the jacket and pipe 19.

In the continuous casting of steel, especially in a multistrand operation, about 60 seconds elapsefrom the time the vessel begins to fill until it is desirable to commence pouring at least one strand. While the vessel is filling, we introduce inert'gas (usually argon) through the porous plug 18 to agitate the molten metal in the nozzle well area. Between five and fifteen seconds before we are ready to cast one strand, we operate valve opening 25 and commence the casting operation.

We prefer to use an oxygenflow rate of from 8 to 10 cubic feet per minute for a period of 7 to 10 seconds. As a specific example, in utilizing our method on a four-strand tundish, we'have injected argon, which is a coolant to the steel, into the nozzle well for up to 4 minutes, then introduced commercially. pure oxygen for just 10 seconds at 8 cubic feetper minute and obtained gas may be insufflated through a porous plugin a sliding gate to stir molten metal within a vessel. However,

practices used heretofore have not successfully overcome. the problem of failure of gates to openproperly.

It is the principle object of our invention to provide a method of for insuring the full opening of a nozzle of an intermediate vessel, such as a tundish, to assure a proper pouring stream.

It is also an object of our invention to provide a method of for opening a nozzle of an intermediate vessel, regardless of whether such nozzle is totally or partially blocked by solidified metal. The single FIGURE is a partly diagrammatic cross section through the nozzle of a bottom-pour intermediate vessel equipped with a sliding gate which employs a permeable refractory block in the gas passageway beneath the vessel nozzle and includes our gas-injection apparatus.-

Vessel 10 has a refractory lining 11 for receiving molten metal. The bottom wall of the vessel has a well or recess 12 and an outlet opening 13 and carries a refractory nozzle plate 14 fixed to its underside aligned with the opening. A sliding gate closure member 15 is mounted beneath the nozzle plate. The gatecan be supported and operated in any desired manner, hence, we have not shown the supporting and operatingmecha nism. The gate includes a solid refractory block 16, a surrounding steel jacket 17, and a gas-permeable refractory plug 18 centered in the upper portion of block 16. A pipe 19 is affixed at its upper end to jacket 17 whichforms withplug 18 a cylindrical gas distribution chamber 20. Pipe 19 extendsto sources Zland 22 of inert gas and oxygen rich gas respectively, either of which can be admitted thereto through a three-way a' free-flowing stream'having good stream characteristics.

The foregoing conditions are critical for the successful practice of our invention. A flow rate of oxygen of less than 5 cubic feet per minute or for a time of less than 5 seconds does not insure that a nozzle will open. Conversely, a flow rate greaterthan 15 cubic feet per minute of oxygen or for a time greater than 15 seconds overheats the steel, and upon teeming the metalinto the mold, the steel may melt the chill pins in the mold stool on contact. Thus, when downward movement of the starterbaris initiated, the mold stool will separate from the casting andthe entire heatmay be lost. Further, excessive oxygen oxidizes the carbon in the steel to carbon dioxide, ca'usinghit to leave the steel as a gas. When elementsthat'form oxides in thesteelarelost, the solidification rate isreducedand breakouts below the mold are not only common, but-arealmostcertain.

plate 14 is made of zirconia, which is only efiectiveto about 3,000F, above whichtemperature it willbecome eroded. Oxygen flow throughthe molten metal inthis region will burn out the zirconia insert if theuppermost diameter of the porousplugisequal to or greater than that of the opening of the zirconiainsert.

Prior to our invention, it was necessary to preheatthe nozzle well to about 2,400F toinsure sufficient heat in the well to prevent the freezing of steel at thebeginning of introduction of steel to theintermediate'vessel. Un-

Although the drawing shows a porous plug gate used on a-singlenozzle intermediate vessel, it iseven' more 3' 4 advantageouslyused in accordance with our invention e. injecting at least enough oxygen-rich gas at a' rate on a multiple-nozzle vessel. of 5 to about 15 scfm into the steel in the vessel It can readily be seen from the foregoing that we have through said plug for a period of from 5 to about invented a method of opening the nozzle of an interme- 15 seconds immediately after termination of inert diate vessel at any time, regardless of whether such 5 gas injection to superheat the steel in the region of nozzle is blocked by solidified metal. the outlet and remove any skull which has formed;

We claim: and l. A method of handling liquid steel in an intermedif. immediately opening the gate and teeming the steel ate vessel in preparation for teeming the steel into a from the vessel into the mold at the conclusion of continuous-casting mold, said method comprising: 0 the step of injecting oxygen-rich gas. 4

a. closing the outlet of the vessel with a slidable gate 2. A method according to claim 1 wherein said oxywhich has a porous plug aligned with the outlet; gen-rich gas is commercially pure oxygen. b. introducing liquid steel to the vessel; 3. A method according to claim 2 wherein oxygen is c. injecting inert gas to the steel in the vessel through injected at a rate of 8 to 10 scfm.

said plug to agitate the steel while it is introduced 4. A method according to claim 2 wherein oxygen is until shortly before teeming is to begin; injected through said plug for a period of from 7 to 10 d. terminating inert gas injection within about 15 secseconds.

onds of the time teeming is to begin; 5*

The first inventor's T UNITED STATES PATENT OFFICE CERTHHCATE(HTCORRECTHMN Patent No. 7 lnvannr(s) Sigmund L. Andrzejak et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

name should read Sigmund L; Andrzejak Signed and sealed this 29th day of October 1974.

{SEAL} Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC 60376-P69 us sovcwuem' PRINTING O FlCE: 56g 93 0 FORM P0-1050 (10-69) 

1. A method of handling liquid steel in an intermediate vessel in preparation for teeming the steel into a continuous-casting mold, said method comprising: a. closing the outlet of the vessel with a slidable gate which has a porous plug aligned with the outlet; b. introducing liquid steel to the vessel; c. injecting inert gas to the steel in the vessel through said plug to agitate the steel while it is introduced until shortly before teeming is to begin; d. terminating inert gas injection within about 15 seconds of the time teeming is to begin; e. injecting at least enough oxygen-rich gas at a rate of 5 to about 15 scfm into the steel in the vessel through said plug for a period of from 5 to about 15 seconds immediately after termination of inert gas injection to superheat the steel in the region of the outlet and remove any skull which has formed; and f. immediately opening the gate and teeming the steel from the vessel into the mold at the conclusion of the step of injecting oxygen-rich gas.
 2. A method according to claim 1 wherein said oxygen-rich gas is commercially pure oxygen.
 3. A method according to claim 2 wherein oxygen is injected at a rate of 8 to 10 scfm.
 4. A method according to claim 2 wherein oxygen is injected through said plug for a period of from 7 to 10 seconds. 